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1 Geologia Sudetica

1 2004

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In situ growth of monazite in anchizonal to epizonal mudrocks: first record from the Variscan accretionary prism of the Kaczawa Mountains, West Sudetes, SW Poland

Kryza R., Zalasiewicz J. A., Charnley N., Milodowski A. E., Kostylew J., Tyszka R.

Geologia Sudetica

2004

Vol. 36

39-51

We report the first occurrence of diagenetic or low grade metamorphic monazite from the Palaeozoic mudrock successions of the Kaczawa Complex of the West Sudetes, Poland. Where observed in relation to the enclosing mudrock, this monazite comprises tiny irregular grains, less than 20 microns in diameter, intergrown with the surrounding matrix minerals. This monazite resembles previously described examples of diagenetic monazite from elsewhere in the world in mostly possessing low contents of Th and U but differs in forming much smaller grains, which show only slight zonation of rare earth elements (REEs). Some of the monazite grains studied also appear to have formed synchronously with the cleavage, perhaps a function of early deformation and fluid release in an accretionary prism environment. Relatively Th-rich cores, and an association with altered detrital biotite in some instances, suggests that at least some of the in situ monazite growth might have taken place as overgrowths on primary detrital monazite particles.